People who are HIV-positive are especially vulnerable to a strain of tuberculosis that has an alarmingly high fatality rate, the World Health Organization has warned. An outbreak of the disease has been discovered in South Africa, and health officials are worried it may be spreading.

Fifty-two of the 53 people with confirmed diagnoses of extremely drug-resistant TB (XDR-TB) reportedly have died. All 53 also had either tested positive for HIV or were suspected of being HIV positive.

TB has been increasing in recent years where AIDS is prevalent, because people with compromised immune systems are less able to fight off infections.

South Africa is second only to India in the number of HIV-positive individuals, with 5.5 million members of the population of 44 million affected. The death toll from the disease is estimated at 900 per day.

Although Dr. Moll has prescribed antiretroviral drugs to about 1,300 people, he estimates that as many as 10,000 to 12,000 more are going untreated.

When he noticed that people who had responded well to antiretrovirals were nevertheless dying, he suspected that he was dealing with XDR-TB, according to press reports. Testing confirmed his suspicion.

The true extent of the XDR-TB outbreak cannot be calculated, Dr. Moll told reporters, because the tests to identify it are expensive and unavailable in many areas. Because miners are highly mobile, he believes it may have spread throughout the country.

Last week, the World Health Organization warned that people could be dying from the new strain in places where there is no health system capable of finding and diagnosing it.

XDR-TB has been found all over the world, most often in the countries of the former Soviet Union and in Asia.

Officials of the World Health Organization and the South African Medical Research Council have been meeting in South Africa this week to develop a plan for controlling the latest outbreak.